Spinal Muscular Atrophy (SMA) is the leading genetic cause of death in infancy. It is a devastating disease that leads to progressive loss of those nerve cells that control our muscle bulk and movement. Patients develop increasing weakness in all muscles, eventually including those needed for breathing. In more than half of patients, SMA starts in infancy and typically leads to death within the first 2 years of life. In others, the disease begins in childhood and leads to significant disability.